[P-EM09] Dynamics of Magnetosphere and Ionosphere

[PEM09-03] Fast Magnetic-Field Annihilation in Electron-scale Current Sheet in Earth's Magnetotail

*長谷川 洋¹、Denton Richard²、Genestreti Kevin³、中村 琢磨⁴、Phan Tai⁵、中村 るみ⁴、Hwang Kyoung-Joo⁶、Ahmadi Narges⁷、Shi Quanqi⁸、Hesse Michael⁹、Burch James⁶、Webster James⁶、Torbert Roy¹⁰、Giles Barbara¹¹、Gershman Dan¹¹、Russell Christopher¹²、Strangeway Robert¹²、Wei Hanying¹²、Lindqvist Per-Arne¹³、Khotyaintsev Yuri¹⁴、Ergun Robert¹⁵、斎藤 義文¹ (1.宇宙航空研究開発機構宇宙科学研究所、2.ダートマス大学、3.サウスウェスト研究所ダーラム、4.オーストリア科学アカデミー、5.カリフォルニア大学バークレー校、6.サウスウェスト研究所サンアントニオ、7.コロラド大学大気宇宙物理学研究所、8.山東大学、9.ベルゲン大学、10.ニューハンプシャー大学、11.NASAゴダード宇宙飛行センター、12.カリフォルニア大学ロサンゼルス校、13.スウェーデン王立工科大学、14.スウェーデン宇宙物理学研究所、15.コロラド大学天体物理学惑星科学科)

キーワード：磁気リコネクション、磁気圏尾部、磁場消失

Magnetic reconnection in current sheets is the key to fast release of magnetic energy in many space and astrophysical plasma systems, such as during magnetospheric substorms, but observations to understand exactly how magnetic-to-electron energy conversion occurs in electron-scale diffusion regions (EDRs), where magnetic topology changes, have been lacking. It is generally believed that EDR has an X-type magnetic-field geometry around which the energy of anti-parallel magnetic fields is mostly converted to the bulk-flow energy of electrons by magnetic tension of reconnected field-lines. We present state-of-the-art analysis of multi-spacecraft observations in Earth's magnetotail of an electron-scale current sheet, which demonstrates that contrary to the standard model of reconnection with an X-type EDR geometry, the fast energy conversion in the detected EDR was caused mostly by magnetic-field annihilation, rather than reconnection. The experimental discovery of the annihilation-dominated EDR reveals a new form of energy conversion in the reconnection process that can occur when the EDR has evolved from the X-type to planar geometry.